Fetal Neonatal Alloimmune Thrombocytopenia (FNAIT) is a rare but potentially very serious condition that occurs in about 1 of 1,000 pregnancies. The condition is characterized by destruction of blood platelets in fetuses and newborns due to maternal antibodies that have traversed placenta.

When a fetus or newborn becomes thrombocytopenic, it is at risk of intracranial hemorrhage that may result in lifelong disability or death. This is seen in 1 in 10,000 pregnancies which amounts to around 1,000 severely affected babies in the US and EU per year. Currently no satisfactory preventive measures or treatment exist for this rare but potentially life-threatening condition.

FNAIT is most commonly caused by incompatibility between mother and fetus for the Human Platelet Antigen-1a (HPA-1a).